EASTMAN : CAEBONIFEKOUS SHARKS. 69 



in Campodus may to all intents and purposes be considered as teeth, which 

 probably formed a mosaic-like pavement. It would appear very doubt- 

 ful, however, if these outgrowths of dentine in tlie present specimen ever 

 functioned as teeth, although they may have served as a sort of cingu- 

 lum ; and their origin is probably attributable to an excessive supply of 

 dentine-forming material, which was deposited adjacent to the larger 

 series. That they are closely related to the principal teeth is evident 

 from the fact that they partake of the same curvature toward the front 

 as these. One of the distinguishing characters of Karpinsky's genus 

 consists in the presence of a double groove extending along the lateral 

 faces of the crown near the base. Nothing of this nature appears in the 

 present example, nor in either of the other species of Campyloprion. 



The last point we have to consider is the base, by which is meant the 

 mass of vasodentin e that served as a common support for the series. 

 Just as the teeth are fused into a continuous series, and their extremities 

 pass by insensible gradations into a common base, so the latter may be 

 said to correspond, in part, £.h least, to fused roots. We say "fused," for 

 the reason that no traces of segmentation are visible : a condition which 

 is also true of Helicoprion, but not of Edestus, although in the latter 

 genus the basal segments are sometimes obscure. As in the other species 

 of Campyloprion, and also in the completely coiled genus, the base is 

 channelled below by a longitudinal canal of considerable size. The dimen- 

 sions and form of cross-section of this channel appear to have been about 

 the same as in C. davisii and Helicoprion bessonowi, although compari- 

 sons are difficult, owing to mechanical compression and partial removal 

 of the latei'al walls. Longitudinal striae extending along the base, and 

 also a generally perforated appearance, such as are here in evidence, are 

 characters not uncommonly presented by the roots of sharks' teeth, and 

 are correlated with the attachment of the series in the supporting sym- 

 physial cartilage. The enormously developed basal segments (roots) 

 of Edestus exhibit a more vascular structure than the compact vasoden- 

 tine base of Campyloprion. 



Comparison of Genera possessing an Edestus-like form of 



Dentition. 



The principal characters of the four genera of Cestraciont sharks 

 whose dentition has been described in the preceding pages, may be 

 summarized as follows : 



VOL. XXXIX. — NO. 3 2 



